[Mimedefang] can't delete recipients

[An.H.Nguyen]

Can some body tell me what's wrong with my filter code below....
I want to delete all the recipients but it does not do so.
(the add_recipient does work, but the delete does not work...)
When I sent a test message, I receive it at both the original recipient and 
spamtrap..
Don't know what's could be wrong... I've searched and searched and tested, 
but no solution...
Thanks,
An Nguyen
==============================
sub filter_end ($) {
    my($entity) = @_;
    return if message_rejected();

    $ecardspam = "You've received a";
        if ($Subject =~ m/$ecardspam/) {
         my $recip;
         foreach $recip ($Recipients) {
         delete_recipient($recip);
        }
         add_recipient('spamtrap at domain.com');
        }
===================================